Quiz 4-2 - Subnet - 1 Hour @🏠

Introduction

Subnet masks are used to partition networks logically so that the size and reach of a network can be controlled through configuration. Watch the following video to learn more. 

Subnet Mask Video

Quiz

If you have any questions about the information above check out the notes below or contact your instructor.

Now, it's quiz time. Remember, you will want to use a subnet mask calculator to help with your calculations. This can be a subnet mask calculator downloaded to your own device or one of the many calculators that can be located using Google. 

More Subnet Mask Information

The subnet mask is used to separate networks. The subnet mask performs a "bitwise AND" on both IP addresses to determine if they are on the same network and can communicate with each other or not.

A subnet mask determines what network an IP address is on and who they can communicate with. Some common subnet masks are 255.255.255.0. Another common mask is 255.255.0.0.

For a bitwise AND, basically you will multiply one bit by another bit and put it in the result. A bitwise AND works as follows:

This is a bitwise AND on 255 and 192. 255 in binary is 11111111. 192 in binary is 11000000.

Now we will do 240 bitwise with 192.  240 in binary is 11110000. 192 in binary is 11000000.

In order for an IP address to talk to another IP address, the results of the subnet mask must match. An example is shown below.

The above results match so these the addresses 192.168.83.10 and 192.168.83.200 can communicate.

The results of the subnet applied to octet three do not match, and, therefore, addresses 192.168.83.10 and 192.168.84.101 cannot communicate.  In order for them to communicate they need a router or layer 3 switch.

We use a subnet in order to allow devices to communicate together.

This is because you cannot assign 0 or 255. 0 used to define the network and 255 is the broadcast address. But what if I need more than 254 devices? That is when we expand our network to include more addresses. We do this by changing our subnet. How do we know how to open our network up? Here is a simple method:

1. There are 254 devices per each network.
2. Take the number of devices wanted and divide by 254.
3. Round the above value to the nearest multiple of 2 up to 128.  (i.e., 2,4,8,16,32,64,128).
4. Take the rounded answer from step 3 and subtract it from 256.
5. This is your 3 octet value.